1. Field of the Invention
The present invention relates to a magnetostrictive stress measurement apparatus and more specifically to a stress measurement apparatus for simultaneously measuring both axial and torsional stressess producerd in a shaft made of a magnetostrictive material.
2. Description of the Prior Art
The present invention is relevant to a pending application (U.S. Ser. No. 011,330) filed Feb. 5, 1987 by the same applicant, entitled MAGNETOSTRICTIVE DEVICE FOR MEASURING TORSIONAL TORQUE.
In the device disclosed in the above application, two, first and second, sensing segment areas for detecting torsional stress produced in a shaft to be measured on the basis of magnetostrictive effect are arranged in V-shaped on the circumferential surface of the shaft at a predetermined angle with respect to the axial direction of the shaft, and a pair of magnetizing coil and detecting coil are loosely arranged around the first and second sensing segment areas. Therefore, when a torsional stress is produced in the shaft under the condition that current is passed through each of these coils, since each inductance of the two coils changes on the basis of magnetostrictive effect at the first and second sensing segment areas, it is possible to separately measure the magnitude and the direction of only a torsional stress produced in the shaft on the basis of change in inductance of each detecting coil.
The above-mentioned magnetostrictive stress measurement apparatus can be mounted on an industrial robot for effecting automated grinding work, for instance. In this case, the first and second sensing segment areas are formed on the outer circumferential surface of a motor shaft provided with a grinding stone at a free end thereof, and a sensor signal representative of a torsional stress produced in the motor shaft is inputted to a robot controller to control the motor speed, for instance.
In the above-mentioned magnetostricitve device, however, although a torsional stress produced in the shaft can be measured, since it is impossible to simultaneously measure the magnitudes and directions of both axial and torsional stress produced in the motor shaft to be controlled, there exists a problem in that it is impossible to appropriately control the pressure of the grinding stone against a workpiece to be ground.